1. Field of the Invention
The present invention relates to an image forming apparatus for secondary-transferring a toner image, which is primary-transferred from an image bearing member to an intermediate transfer member at a primary transfer portion, to a recording material at a secondary transfer portion, and more particularly to a electrically discharging mechanism for an intermediate transfer member, which is necessary when continuous image formation is performed.
2. Description of the Related Art
An image forming apparatus has been in practical use, which forms a full-color image by using a highly resistant (and insulative) intermediate transfer member left in a charged state after one rotation thereof in which an image is formed. The highly resistant intermediate transfer member has a high capability to hold electric charge given during transfer, which suppresses a toner scattering phenomenon that disturbs a transferred toner image.
However, repeated image formation by such a image forming apparatus causes charge-up where the charging potential of the intermediate transfer member gradually increases. Consequently, in order to transfer the toner image, a primary transfer voltage applied to a primary transfer member by a primary transfer power source and a secondary transfer voltage applied to a secondary transfer member by a secondary transfer power source need to be increased.
Accordingly, in the conventional image forming apparatus that uses the highly resistant intermediate transfer member, various electrically discharging apparatuses have been disposed between a secondary transfer portion and a primary transfer portion to prevent the intermediate transfer member from being charged up.
Japanese Patent Application Laid-Open No. 2001-265095 discusses a full-color image forming apparatus of a tandem intermediate transfer system which includes a plurality of photosensitive drums (image bearing members) in a linear section of an intermediate transfer belt. This image forming apparatus includes a electrically discharging apparatus on a downstream side of a secondary transfer portion, and a electrically discharging member of the electrically discharging apparatus, which is in contact with the intermediate transfer belt, is applied a voltage in which a DC voltage and AC voltage are superposed. However, in the image forming apparatus discussed in Japanese Patent Application Laid-Open No. 2001-265095, the electrically discharging apparatus is an obstacle for downsizing the image forming apparatus.